1. Field of the Invention
The present invention relates to a shift control system for a continuously variable transmission and, more particularly, to a shift control at the time of a kick-down operation in a continuously variable transmission.
2. Description of the Prior Art
A conventional shift control system for a continuously variable transmission is disclosed in Japanese Patent Application Laid-open No. 9-310757. In this conventional system, the driver""s intention of accelerating is detected on the basis of an accelerator pedal opening, and a target gear ratio of the continuously variable transmission is calculated according to a vehicle speed and a throttle opening. The throttle opening is corresponding to the accelerator pedal opening.
If the accelerator pedal opening exceeds a predetermined value, moreover, it is determined that the driver has demanded a rapid acceleration, and thus kick-down acceleration is performed.
According to the aforementioned prior art, however, the kick-down acceleration is determined depending on whether the accelerator pedal opening exceeds a predetermined value. Therefore, when the driver depresses the accelerator pedal in a large amount without intention of a rapid acceleration, it is erroneously determined that the driver demanded a rapid acceleration. This causes the engine speed to increase beyond the driver""s intention. In addition, there is a problem of the occurrence of excessive noise accompanying the increase of the engine speed.
The present invention has been made in view of the aforementioned problem, and its object is to provide a shift control system for a continuously variable transmission capable of more accurately determining acceleration intention of a driver without determining it on the basis of an accelerator pedal opening (or depression) only.
According to one aspect of the invention, a shift control system for a continuously variable transmission which has target gear ratio corresponding value calculating means for calculating a target gear ratio corresponding value of the continuously variable transmission according to at least a throttle opening, and shift control means for controlling a gear ratio of the continuously variable transmission so that the target gear ratio corresponding value can be obtained, comprises reactive force applying means disposed on an accelerator pedal and applying a reactive force, which increases according to an increase of the accelerator pedal opening, to a pedal depression force of a driver in a large accelerator pedal opening range.
According to the prior art, even in case where the driver has no intention to accelerate substantially, the accelerator pedal is smoothly opened, and the kick-down acceleration is performed as a result.
This problem may arise in case where the driver does not think xe2x80x9cincreasing the accelerator pedal openingxe2x80x9d means xe2x80x9cacceleratingxe2x80x9d but he thinks xe2x80x9cstrongly depressing the accelerator pedal (or increasing pushing force)xe2x80x9d means xe2x80x9cacceleratingxe2x80x9d. In this case, if the accelerator pedal opening is large even though the accelerator pedal is not strongly depressed, a rapid acceleration may be caused.
In the invention, on the contrary, the accelerator pedal is provided with the reactive force applying means for applying reactive force, which increases according to the increase of the accelerator pedal opening, to depression force exerted on the accelerator pedal by the driver in a large accelerator pedal opening range. Thus, when the driver depresses the accelerator pedal, the reactive force is applied to the driver""s depression force at the time the accelerator pedal opening exceeds a predetermined opening. Therefore the accelerator pedal is not depressed more than the driver""s intention, and a stable acceleration can be attained.
Preferably, the reactive force applying means is provided with a kick-down detector for detecting a kick-down accelerating operation of the driver, and the target gear ratio corresponding value calculating means has:a first target gear ratio corresponding value calculation map for an ordinary control in which a target primary revolution speed in relation to a vehicle speed is set for each throttle opening and a second target gear ratio corresponding value calculation map for kick-down acceleration in which a target input speed is set to a higher value relative to the target gear ratio corresponding value calculation map for an ordinary control. And the shift control means controls a gear ratio so as to obtain a target gear ratio corresponding value-which is calculated by using the first map for an ordinary control when the kick-down detector detects no kick-down operation and so as to obtain a target gear ratio corresponding value which is calculated by using the second map for kick-down acceleration when the kick-down detector detects a kick-down operation.
When the accelerator pedal is more strongly depressed against reactive force applied by the reactive force applying means, it is determined that the driver intends to accelerate rapidly. In this case, controls suiting the driver""s intention can be performed by using the target gear ratio corresponding value calculation map for kick-down acceleration.
Further preferably, the kick-down detector is a push type kick-down switch provided in an elastic member and is pushed by the elastic member which is deformed to a predetermined amount by a pushing force given by the accelerator pedal, and thereby detecting a kick-down accelerating operation.
By using such type of kick-down switch, the driver""s intention to accelerate can be easily determined without requiring a complicated arrangement.
Further preferably, the shift control means increases a shift speed for changing a gear ratio of the continuously variable transmission when performing a shift control by using the second map for kick-down acceleration.
A shift speed for changing a gear ratio of the continuously variable transmission is increased when the shift control is performed using the second map for kick-down acceleration. When a kick-down acceleration is chosen, the driver is demanding a rapid acceleration. By attaining a target gear ratio faster, therefore, acceleration excellent in response is realized.
Still further preferably, the shift control means adds a correction pressure to a line pressure for an ordinary control when performing a gear ratio control at a high shift speed.
In case of using the belt-type continuously variable transmission, the pulley pressure needs to be rapidly increased for changing the gear ratio at a high speed. In this case, since the correction pressure is added to the line pressure for an ordinary control, the target gear ratio can be attained with good response.
The above and further objects and features of the invention will be more fully apparent from the following description when the same is considered with reference to the accompanying drawings.